The present invention relates, in general, to cyclone separators for separating steam from steam/water mixtures, such as in a steam drum of a boiler.
Steam/water mixtures are commonly produced by boilers used in the industrial processes such as the pulp and paper industry, and in the utility power generation industry. The separated steam may be used for process heating or other applications known in these industrial applications, or it may be used as the driving force of steam turbine generators used in electrical power generation. For additional information concerning steam/water cyclone separators as employed in steam drums, the industrial or utility power generation settings in which they may be applied, the reader is referred to Steam/its generation and use, 41st Edition, Kitto and Stultz, Editors, Copyright© 2005, The Babcock & Wilcox Company.
Various types of devices have been developed to separate steam from steam/water mixtures. The following discussion is merely intended to be illustrative of some of these developments.
U.S. Pat. No. 2,271,634 to Fletcher discloses a cylindrical cyclone separator having a circular whirl chamber, a tangential inlet, a central steam outlet located at the top of the circular whirl chamber, and a water outlet located at the bottom of the whirl chamber. To prevent water from being discharged through the steam outlet, means are provided for increasing the downward component of the incoming stream of steam and water mixture. This means is a segmented plate having downwardly and rearwardly inclined edges that causes the incoming steam and water mixture to be deflected downwardly towards the water outlet of the separator.
U.S. Pat. No. 2,293,740 to Kooistra discloses a similarly designed cyclone separator that does not utilize the segmented plate but rather employs a bottom cup at the bottom of the whirl chamber which confines the steam to the upper portion of the whirl chamber and prevents it from passing down into the separated water as it discharges from the whirl chamber, into the drum.
U.S. Pat. No. 2,298,285 to Fletcher discloses another variation of the cylindrical cyclone separator this time employing a rim or cap on top of the cyclone separator steam outlet together with the segmented plate. The rim acts to enhance separation of water and reduction of pressure drop in the separator.
U.S. Pat. No. 2,321,628 to Rowand et al. discloses a cyclone separator which is similar to the present application. The circulator whirl chamber in this reference is the frustum of a cone at the upper portion and substantially cylindrical at the lower portion where the water is discharged. Again, a tangential inlet is employed to deliver the steam water mixture into the cyclone separator, and is of a vertical extent substantially equal to that of the tapered portion of the whirl chamber. The tapered configuration acts to direct the entering steam water mixture into a slightly downward direction to prevent upward spread of the deflected water and enhance separation of the steam therefrom.
U.S. Pat. No. 2,346,672 to Fletcher discloses a substantially cylindrical cyclone separator this time having instead of a tangential inlet a large steam/water inlet which extends over a large fraction of the perimeter of the cyclone separator. As indicated in the reference, the inlet can extend to approximately ⅓ of the perimeter of the cyclone separator to provide adequate flow capacities. One object is to produce a separator or densifier which operates effectively with low pressure drop so that it can be advantageously used where only a small pressure head is available.
U.S. Pat. No. 2,395,855, to Fletcher discloses a substantially cylindrical cyclone separator having a tangential inlet and where the steam outlet center is located eccentric of the whirl chamber center to effect enhanced separation of steam from the water. This design also employs the segmented plate seen in the previously described patents.
U.S. Pat. No. 2,402,154 to Fletcher and the aforementioned U.S. Pat. No. 2,395,855 are both divisionals of the same application. The U.S. Pat. No. 2,395,855 is drawn to the particular type of fluid separator itself; while the U.S. Pat. No. 2,402,154 is drawn to the combination of this device in a steam generator.
U.S. Pat. No. 2,434,637 to Brister, U.S. Pat. No. 2,434,663 to Letvin and U.S. Pat. No. 2,434,677 to Stillman are all drawn to various aspects of the perforated cone used at the top of the cyclone separator to enhance separation of the steam from the water.
U.S. Pat. No. 2,532,332 to Rowand is drawn to the particular construction of the separators which today are generally considered as secondary scrubbers.
U.S. Pat. No. 2,732,028 to Coulter is also drawn to a cyclone separator device very similar to that employed at this time. The cyclone separator has the aforementioned frustoconical upper section and generally cylindrical lower section with a tangential steam water inlet located on the side of the frustoconical section. The overall emphasis of this reference is drawn to means of simplifying the construction for accessibility and repair of the elements located in the steam drum. This is accomplished by dividing the steam space in the drum into separate compartments, one or more of which are open to the water space of the drum into the necessary drum safety valves while one or more of the other compartments are open to the steam and water separators of the drum the saturated steam outlets. Partitions are used to accomplish this division and they are effective in maintaining the separation of the drum components during normal operation but are easily broken when the safety valves are opened.
U.S. Pat. No. 2,891,632 to Coulter is drawn to a cyclone steam separator quite similar to that disclosed in the earlier mentioned Fletcher patent (U.S. Pat. No. 2,346,672) with the exception that instead of the steam water inlet being located only approximately along ⅓ of the circumference of the separator, this cyclone separator has the entire circumference provided with an array of vanes that “slice” the incoming steam water mixture into thin sheets to enhance separation of the steam from the water.
U.S. Pat. No. 5,033,915 to Albrecht is drawn to a cyclone steam separator quite similar to that disclosed at this time. The cyclone separator is a modified version of the standard conical cyclone separator that provides a lower pressure drop than the standard conical cyclone for an equivalent number of or an equivalent steam capacity of the separators. The major modification of this separator is that the cyclone separator's tangential inlet has been lengthened by 3 inches. This increase in length increases the cyclone inlet flow area by 28%.
In the late 1980's and early 1990's, The Babcock & Wilcox Company (B&W) performed several steam/water conical cyclone separator tests in order to find ways to improve the performance of the standard conical cyclone separator, particularly ways to increase the separation capacity of the separator without adversely increasing the pressure drop through the cyclone separator. The standard conical cyclone separator 10 is shown in FIG. 1. As part of these tests, the effect of extending the length of the cyclone separator was investigated. It was known that the separation performance and pressure drop through the separator was affected by the design and location of the conical vane bottom plate that is typically located at the inside of the lower conical portion of the separator.
Referring to FIG. 1, the conical steam/water conical separator or separator 10 which may be mounted within a steam drum (see FIG. 10, infra) and having a housing which has an upper conical portion 12 and a lower cylindrical portion 14. A steam/water inlet 16 having an axial length provides a means for introducing a steam/water mixture tangentially into the upper conical portion of the separator 10. The steam/water mixture is separated into steam and water by swirling the mixture at high velocity around the interior of the separator 10. The greater mass of the water causes it to move to the outside of the swirling stream leaving a concentration of steam in the central portion. The steam is discharged through an upper cylindrical outlet 17. If desired, the separated steam discharged through outlet 17 may be further treated by conventional scrubbers and other equipment (see FIG. 10, infra) to remove water droplets which may still be present. The water which has been removed from the mixture is discharged from the separator 10 through a lower cylindrical portion 14 and a ring shaped, conical vane plate 18 located at the bottom of the separator 10. The separator 10 has an overall axial length of about 20″.
The above basic description of the operation of a steam/water conical cyclone separator generally applies to other steam/water conical cyclone separators described in the balance of the present disclosure.
As part of the testing, it was discovered that the length of the cyclone separator 10 could be increased by up to an additional 6 to 8 inches with the conical vane plate 18 remaining at the bottom of the cyclone separator 10. This is accomplished by making the cylindrical portion 14′ 6 to 8 inches longer, and this separator 20 is shown in FIG. 2. Separator 20 thus has an overall axial length of about 28 inches. The surprising results from the testing of the extended length separator 20 with the longer cylindrical portion 14′ were that the performance and pressure drop aspects of the separator 20 were maintained or equivalent to the standard conical cyclone separator 10. See FIGS. 3, 4 and 5.
The steam/water conical cyclone separator 30 of Albrecht is shown in FIG. 6. One difference between the separator 30 and the separators 10 and 20 is that the steam/water inlet of separator 30, designated 16′, partially extends into the lower cylindrical portion 14, with an overall length also about 3″ longer in the cylindrical portion than the separator of FIG. 1. Similar performance and pressure drop results to those described in the paragraph immediately above were also observed when an extended length lower cylindrical portion 14′ was applied to that type of cyclone separator design; see FIG. 7. The separator of FIG. 7 has an overall length of about 28 inches.
As mentioned above, the main purpose of the testing that was done in the late 1980's and early 1990's was to obtain a lower pressure drop cyclone separator. However, there was also a need to gain an understanding of the effects of extending the length of the separator and the importance of the location of the conical vane plate 18. Since the market at the time was requiring larger water volumes in the steam drum, the lengthening of the cyclone separator was a very valuable technique for increasing the water inventory in the steam drum without increasing the diameter of the steam drum. The question that the testing investigated was the importance of the location of the conical vane plate 18 when the cyclone separator was extended. By increasing the overall length of the cyclone, the location of the conical vane plate 18 was considered to be a very important component of the separator design that strongly affected the performance and separation efficiency of the separator. This was the conclusion that was reached in past cyclone separator studies that were done before the 1980's (some of which go back to the 1930's and this knowledge has been passed down through technical discussions rather than through documented results). So if the conical vane plate was positioned at a different location than what the separator of FIG. 1 used, the performance of the separator was questioned. Since the testing showed basically no difference, the FIG. 2 and FIG. 7 cyclone separators were developed and offered as boiler components for B&W steam drums. However, the performance results of placing the conical vane plate in a cyclone separator where the separator length is increased by more than six inches are uncertain. To the best of the present inventors' knowledge, no B&W steam/water conical cyclone separators have utilized only an open additional length conical extension on the bottom of the conical cyclone separator. All extended length cyclone separators have incorporated the conical vane plate at the bottom of the separator.